Low profile, high stretch knit prosthetic device

ABSTRACT

A radially expandable stent-graft endoprosthesis is provided. The graft included in the stent-graft is a knitted tubular structure circumferentially disposed and securably attached to the stent. The knitted tubular structure has a knit pattern of interlacing yarns in an Atlas or a modified-Atlas pattern to provide greater than 150 percent longitudinal stretchability. A knitted tubular graft and a knitted medical fabric with greater than 150 percent longitudinal stretchability are also provided.

FIELD OF INVENTION

The present invention relates generally to a tubular implantableprosthesis having a knitted textile structure. More particularly, thepresent invention relates to an endoprosthesis with a knitted textilestructure having increased longitudinal stretchability.

BACKGROUND OF RELATED TECHNOLOGY

An intraluminal prosthesis is a medical device used in the treatment ofdiseased blood vessels. An intraluminal prosthesis is typically used torepair, replace, or otherwise correct a diseased or damaged bloodvessel. An artery or vein may be diseased in a variety of differentways. The prosthesis may therefore be used to prevent or treat a widevariety of defects such as stenosis of the vessel, thrombosis, occlusionor an aneurysm.

One type of intraluminal prosthesis used in the repair of diseases invarious body vessels is a stent. A stent is a generally longitudinaltubular device formed of biocompatible material which is useful to openand support various lumens in the body. For example, stents may be usedin the vascular system, urogenital tract and bile duct, as well as in avariety of other applications in the body. Endovascular stents havebecome widely used for the treatment of stenosis, strictures andaneurysms in various blood vessels. These devices are implanted withinthe vessel to open and/or reinforce collapsing or partially occludedsections of the vessel.

Stents generally include an open flexible configuration. Thisconfiguration allows the stent to be inserted through curved vessels.Furthermore, this configuration allows the stent to be configured in aradially compressed state for intraluminal catheter implantation. Onceproperly positioned adjacent the damaged vessel, the stent is radiallyexpanded so as to support and reinforce the vessel. Radial expansion ofthe stent may be accomplished by inflation of a balloon attached to thecatheter or the stent may be of the self-expanding variety which willradially expand once deployed. Structures which have been used asintraluminal vascular grafts have included coiled stainless steelsprings; helically wound coil springs manufactured from a heat-sensitivematerial; and expanding stainless steel stents formed of stainless steelwire in a zig-zag pattern. Examples of various stent configurations areshown in U.S. Pat. Nos. 4,503,569 to Dotter; 4,733,665 to Palmaz;4,856,561 to Hillstead; 4,580,568 to Gianturco; 4,732,152 to Wallstenand 4,886,062 to Wiktor, all of whose contents are incorporated hereinby reference.

A graft is another commonly known type of intraluminal prosthesis whichis used to repair and replace various body vessels. A graft provides alumen through which blood may flow. Moreover, a graft is oftenconfigured to have porosity to permit the ingrowth of cells forstabilization of an implanted graft while also being generallyimpermeable to blood to inhibit substantial leakage of bloodtherethrough. Grafts are typically tubular devices which may be formedof a variety of materials, including textile and non-textile materials.

A stent and a graft may combined into a stent-graft endoprosthesis tocombine the features thereof. The graft, however, in the stent-graftendoprosthesis should comply with the implantation requirements of thestent which often include collapsing the stent for placement at animplantation site and expansion of the stent for securement thereat.Grafts which cannot easily accommodate the longitudinal and/or radialdimensional changes from a unexpanded or collapsed state to an expandedstent often complicate the implantation of the stent-graft. Forinstance, some grafts are folded in the collapsed or unexpanded stateand must be subsequently be unfolded to accommodate the expanded stent.The unfolding of the graft, however, often complicates the placement ofthe graft on the stent and the implantation of the stent-graft itself.Alternatively, noncontiguous grafts have been used with expandablestent-grafts. Upon expansion of the stent, however, portions of thenoncontiguous graft often separate to accommodate the stent expansion.This separation leaves gaps in the graft structure thereby permittingthe leakage of blood through these gaps.

Thus, there is a need for a graft that compliments the implantation ofan expandable stent of a stent-graft endoprosthesis. In particular,there is need for a graft that is securably attached to the stent inboth the expanded and unexpanded state without complicating themechanical dynamics of the stent or the graft.

SUMMARY OF THE INVENTION

The present invention provides an implantable tubular prosthesis havinga radially expandable tubular stent structure having a first diameterand capable of longitudinal expansion or contraction to achieve a seconddiameter which is different from the first diameter and a tubularknitted tubular graft circumferentially disposed and securably attachedto the stent. The graft has a pattern of interlaced wale and courseyarns in a knit pattern to permit longitudinal expansion or contractionof the graft substantially consistent with the longitudinal expansion orcontraction of the stent.

The prosthesis of the present invention is capable of longitudinalexpansion from 50 to 200 percent by length from a quiescent state.Alternatively, the prosthesis of the present invention is capable of 50to 200 percent longitudinal contraction by length to achieve asubstantially quiescent state from an unexpanded state. Furthermore, thetextile graft of the present invention is substantially fluid-tight inits quiescent state.

To achieve such a degree of longitudinal expansion or contraction thetextile graft includes a stretchable knit pattern. The pattern is a warpknitted pattern having a set yarns diagonally shifted over one or moreyarns to form a loop between engaging yarns. Furthermore, the engagingyarns alternately form open loops where the engaging yarns do not crossover themselves and closed loops where the engaging yarns cross overthemselves. The knit pattern is generally described as a Atlas or anmodified-Atlas knit pattern. Such patterns depart a high degree offlexibility and stretchability to the textile graft of the presentinvention.

The knit pattern further includes a plurality of front and back yarnsformed from single stitches, where the single stitches are deposed in aplurality of stitch repeating patterns. A first stitch has a repeatingpattern traversing diagonally by two or more needle positions and asecond stitch has a repeating pattern alternatively traversingdiagonally by three or more needle positions and by one needle position.

In one aspect of the present invention an implantable tubular prosthesiscapable of longitudinal expansion from a quiescent state to an elongatedstate in provided. The prosthesis includes a radially contractible andlongitudinally expandable tubular stent having a quiescent diameter andquiescent length capable of longitudinal expansion to the elongatedstate having an elongated length and a contracted diameter, wherein theelongated length is greater than the quiescent length and the contracteddiameter is smaller than the quiescent diameter, and further wherein thestent is capable of resiliently returning from the elongated state tothe quiescent state. The prosthesis further includes a tubular knittedtubular graft circumferentially disposed and securably attached to thestent in the quiescent state. The graft has a pattern of yarnsinterlaced into stitches in a knit pattern capable of resilientlongitudinal elongation and resilient radial contraction of the graft tothe elongated state. Furthermore the graft has from 400 to 900 stitchesper square centimeter to provide compliancy in the quiescent state.

In another aspect of the present invention an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent as described above and a tubular knittedtubular graft having a warp knitted pattern of yarns forming a textilelayer having an interior surface and an exterior surface, whereininterior yarns predominate the interior surface and form loops in thelongitudinal direction of the prosthesis, and exterior yarns predominatethe exterior surface and are diagonally shifted over one or more of theinterior yarns in an alternating pattern along a width of the prosthesisto engage the interior yarns. The interior yarn alternately interlacesthe engaging exterior yarn to form open loops where the interior yarndoes not cross over itself and closed loops where the interior yarn doescross over itself

In another aspect of the present invention an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent and a tubular knitted tubular graftcircumferentially disposed and securably attached to the stent in thequiescent state, where the graft has greater than about 350 stitches persquare centimeter in its knit pattern to provide compliancy of the graftand wherein the prosthesis is capable of longitudinal expansion from 50to 200 percent by length.

In yet another aspect of the present invention, an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent and tubular knitted tubular graftcircumferentially disposed and securably attached to the stent. Thegraft has a knit pattern with greater than about 350 stitches per squarecentimeter while also having a wall thickness from about 0.3 to about0.4 millimeters.

In still another aspect of the present invention, an implantable tubularprosthesis capable of longitudinal expansion from a quiescent state toan elongated state includes a radially contractible and longitudinallyexpandable tubular stent and tubular knitted tubular graftcircumferentially disposed and securably attached to the stent, whereinthe stent and the graft are resiliently deformable between the quiescentand elongated states and further wherein the graft non-bulginglycontracts from the elongated state to the quiescent state tocircumferentially abut the stent.

In still yet another aspect of the present invention, an implantabletubular prosthesis capable of radial expansion from a quiescent state toa radially expanded state includes a radially expandable andlongitudinally contractible tubular stent and a tubular knitted tubulargraft circumferentially disposed and securably attached to the stent inthe quiescent state. The graft has a pattern of yarns interlaced intostitches in a knit pattern capable of resilient radial expansion andresilient longitudinal contraction of the graft to the elongated stateand has from 400 to 900 stitches per square centimeter to providecompliancy for the graft in the quiescent state.

In other aspects of the present invention, a non-textile, desirablyePTFE, layer is provided with the endoprosthesis of the presentinvention. Moreover, a textile graft capable of resilient elongation andhaving from 400 to 900 stitches per square centimeter is provided.Furthermore, an implantable medical fabric is provided. The medicalfabric is a knitted textile with a high degree of stretchability becauseof the Atlas and the modified-Atlas stitches used to form the fabric. Amethod for producing the high stretch knit prosthetic device is alsoprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cut-away perspective view of an endoprosthesis ofthe present invention having a stent and a graft both capable oflongitudinal expansion or contraction.

FIG. 2 is a cross-sectional view of the stent-graft of FIG. 1 takenalong the 2—2 axis.

FIG. 3 depicts the stent-graft of FIG. 2 having a longitudinallyexpanded length.

FIG. 4 depicts a wire stent in an expanded state according to thepresent invention.

FIG. 5 depicts the wire stent of FIG. 5 in an unexpanded state.

FIG. 6 depicts a slotted stent in a quiescent state according to thepresent invention.

FIG. 7 depicts the slotted-stent of FIG. 6 in an expanded state.

FIG. 8 is a perspective view of a helical coil formed of a single woundwire.

FIG. 9 is a perspective view of a stent having an elongate pre-helicallycoiled configuration.

FIG. 10 is a perspective view of the stent of FIG. 9 in a radiallyexpanded state.

FIG. 11 is a diagrammatic illustration of a textile portion of the graftof FIG. 1 taken along the 11—11 axis.

FIGS. 12 and 13 depict yarn patterns for the textile portion of FIG. 11.

FIG. 14 is a cross-sectional of the present invention which furtherincludes a layer of e-PTFE.

FIG. 15 is a partial perspective view of a knitted medical fabric of thepresent invention.

FIG. 16 is a photomicrograph showing a longitudinally expanded ePTFEstructure.

FIG. 17 is a photomicrograph of physically modified ePTFE structurehaving enhanced elongation properties as compared to the ePTFE structureof FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses the problems associated with prior artstent-graph endoprosthesis. The stent-graft endoprosthesis of thepresent invention overcomes the disadvantages of presently availablestent-grafts by providing an expandable graft that complements anexpandable stent in both an expanded or contracted state. Furthermore,the graft of the present invention is knitted textile graft whichprovides greater stretchability than previously knitted or woven textilegrafts. Moreover, the knitted textile graft of the present invention hasa porosity to permit the ingrowth of cells for the stabilization ofimplanted endoprosthesis while also being generally impermeable toinhibit substantial leakage of blood therethrough.

FIG. 1 is a depiction of stent-graft 10 of the present invention.Stent-graft 10 is shown as a generally tubular structure with open ends16, 18 to permit the passage of a bodily fluid therethrough. Stent-graft10 includes textile graft 12 and stent 14. Textile graft 12 extendscircumferentially about stent 14. Textile graft 12 is securably attachedto stent 14. The attachment of textile graft 12 to stent 14 may beaccomplished by mechanically securing or bonding the textile graft 12and the stent 14 to one and the other. Mechanical securement includes,but is not limited to, the use of sutures, anchoring barbs, textilecuffs and the like. Bonding includes, but is not limited to, chemicalbonding, for instance adhesive bonding, thermal bonding and the like.

As depicted in FIG. 1, the textile graft 12 circumferentially extendsabout an outer stent surface 20. The present invention, however, is notso limited and other stent-graft configurations may suitably be usedwith the present invention. For instance, textile graft 12 may becircumferentially positioned along an inner surface of stent 14.Moreover, the longitudinal lengths of the stent 14 and the textile graft12 are not limited to substantially similar lengths as depicted in FIG.1. For instance, textile graft 12 may be shorter than stent 14 therebyleaving a portion of stent 14 without being covered by textile graft 12.

FIG. 2 dimensionally depicts the stent-graft 10 of the present inventionafter securement within a bodily lumen (not shown) and FIG. 3dimensionally depicts the stent-graft 10′ prior to securement thereat.To navigate the stent-graft within a bodily lumen the nominal diameter,D₂, of stent-graft 10′ is smaller than the diameter, D₁, of stent-graft10. Correspondingly, the length, L₂, of stent-graft 10′ is larger thanthe length, L₁, of stent-graft 10. The textile graft 12 and the stent 14both conform to these general dimensional depictions for the navigationand securement of stent-graft 10 within a bodily lumen. The textilegraft 12 is elongated or stretched to accommodate the elongatedstent-graft 10′. Correspondingly, textile graft 12 is in a substantiallyquiescent state to accommodate the stent-graft 10 of FIG. 2.

Various stent types and stent constructions may be employed in theinvention. Useful stents include, without limitation, self-expandingstents and balloon expandable stents. The stents may be capable ofradially contracting or expanding, as well, and in this sense can bebest described as radially or circumferentially distensible ordeformable. Self-expanding stents include those that have a spring-likeaction which causes the stent to radially expand, or stents which expanddue to the memory properties of the stent material for a particularconfiguration at a certain temperature. Nitinol is one material whichhas the ability to perform well while both in spring-like mode, as wellas in a memory mode based on temperature. Other materials are of coursecontemplated, such as stainless steel, platinum, gold, titanium andother biocompatible metals, as well as polymeric stents.

The configuration of stent 14 may be of any suitable geometry. As shownin FIG. 4, wire stent 22 is a hollow tubular structure formed from wirestrand 24 being arranged in what can be described as a “Z” or a“zig-zag” pattern. Wire strand 24 may be formed by, for example,braiding or spinning it over a mandrel. Alternatively, wire stent 24 maybe formed from more than one wire strand.

Wire stent 22 is capable of being radially compressed and longitudinallyextended, to yield wire stent 22′, as depicted in FIG. 5, forimplantation into a bodily lumen. The degree of elongation depends uponthe structure and materials of the wire stent 22 and can be quitevaried. For example, the length of wire stent 22′ is from about 50% toabout 200% of the length of wire stent 22. The diameter of wire stent22′ may also be up to several times smaller than the diameter of wirestent 22.

In another aspect of the present invention, a slotted stent 26 is alsouseful as part of the stent-graft 10. As depicted in FIG. 6, slottedstent 26 is suitably configured for implantation into a bodily lumen(not shown). Upon locating the slotted stent 26 at the desired bodilysite, slotted stent 26 is radially expanded and longitudinallycontracted for securement at the desired site. The expanded slottedstent 26′ is depicted in FIG. 7. Slotted stent 26′ is from about 50% toabout 200% greater in radial dimension as compared to slotted stent 26.

Other useful stents capable of radial expansion are depicted in FIGS. 8,9 and 10. As depicted in FIG. 8, stent 28 is a helical coil which iscapable of achieving a radially expanded state (not shown). Stent 29, asdepicted FIG. 9, has an elongate pre-helically coiled configuration asshown by the waves of non-overlapping undulating windings. Stent 29 iscapable of being radially expanded to expanded stent 29′ as depicted inFIG. 10. These helically coiled or pre-helically coiled stents are alsouseful with the practice of the present invention.

The textile graft 12 is a knitted textile graft. Knitting involves theinterlooping or stitching of yarn into vertical columns (wales) andhorizontal rows (courses) of loops to form the knitted fabric structure.Warp knitting is particularly useful with the textile graft 12 of thepresent invention. In warp knitting, the loops are formed along thetextile length, i.e., in the wale or warp direction of the textile. Fora tubular textile, such as textile graft 12, stitches extending in theaxial or longitudinal direction of the tubular textile are calledcourses and stitches extending along the circumference of the tubulartextile are called wales.

Conventional knitted tubular grafts often had to reduce or limit thenumber of courses per unit length to obtain a flexible tubularstructure, i.e., a structure with longitudinal stretchability. Reducingthe number of courses per unit length, however, opens the macroporousstructure of the textile. A macroporous textile structure is notdesirable as a graft because such a structure is not a fluid tightstructure, i.e., blood will flow through the graft. Similarly, if thenumber of wales per unit length was too low, the graft would not sealblood flow. If the number of wales per unit length was too high, thegraft could dilate with time. Thus, conventional grafts were limited bythe total number of courses and wales per unit length, which is referredto as the number of picks per unit area or the pick size.

For example, textile tubular prostheses in a warp-knit or an Atlas-knitwere typically limited to 4 to 16 courses per centimeter (10 to 40courses per inch) and to 4 to 16 wales per centimeter (10 to 40 walesper inch) to provide a longitudinally stretchable tubular structure. Thepick size of these stretchable prostheses were limited to about 16 to 62stitches per square centimeter (100 to 400 stitches per square inch).The textile graft 12 of the present invention is not so limited becauseof the novel knit pattern used to form the graft as compared to moreconventional knit patterns, such as tricot, locknit and the like, oreven previously used Atlas-knits.

Moreover, grafts are sometimes crimped with creases or folds which tendto reduce kinking when the graft is bent. The kinking also allows forsome elongation of the graft, but such a crimped graft would not begenerally useful as a stent-graft because of the gaps that would resultbetween the stent and the crimped graft.

The textile graft 12 is configured to have a high degree ofstretchability. As used herein, the term stretchability and its variantsrefers to a textile capable of substantially reversible elongationbetween a quiescent state and a stretched state. Desirably thestretchability of the textile graft 12 is substantially compatible withthe dimensional changes associated with an expandable stent having botha expanded and an unexpanded or a contracted state as discussed above.Moreover, textile graft 12 is not a crimped graft and does non-bulginglycontract from the elongated state to the quiescent state. The textilegraft 12 substantially abuts the stent along both circumferential andlongitudinal portions of the stent without separating or bulging fromthe stent.

Knitting patterns useful in providing the desired stretchability includethose knitting patterns that are not highly interlaced, such as patternsthat interlace each adjacent back and front yarn. An example of a highlyinterlaced and commonly known knitted pattern is a Tricot or Jerseypattern. In contrast the knitting pattern of the present invention isnot highly interlaced to provide, among other things, the stretchabilityof the textile graft for use with an expandable stent.

FIG. 11 is an illustration of a portion 30 of the textile graft 12 takenalong the 11—11 axis. The knitted portion 30 is characterized as a warpknit atlas pattern. In FIG. 11, needle position in the course direction,i.e., vector 51, are noted by element numbers 32 a through 32 h, andneedle position s in the wale direction, i.e., vector 53, are notedelement numbers 34 a through 34 i. A yarn moves one needle position inthe course direction and one needle position in the wale directionbefore alternately interlacing with adjacent yarns. The needle positionsare indicated by dots 58. For example, yarn 36 c moves in the coursedirection from needle position 32 d to needle position 32 e, from needleposition 32 e to needle position 32 d, from needle position 32 d toneedle position 32 c, from needle position 32 c to needle position 32 d,and then repeats this alternating pattern. As yarn 36 c moves in thecourse direction, it also moves generally in wale direction. Adjacentwales and adjacent courses are interlooped to form a warp knitted atlaspattern. The pattern is further described below in conjunction withFIGS. 12 and 13.

The knitted portion 30 is depicted as a single knitted layer in FIG. 11,however, the textile graft 12 of the present invention is not solimited. For instance, the knitted portion 30 may include more than onelayer of interconnected yarns. In such a multi-layered knitted textile,yarns from one layer are often interlooped with yarns in another layerto form the multi-layered knitted textile.

Textile graph 12 is flat knitted tubular structure to form such aflat-knitted tubular structure, two portions 30 are co-knitted to oneand the other and joined together by border yarns. FIG. 12 depicts theyarn patterns of FIG. 11 by separating front and back yarns from one andthe other to more clearly illustrate the individual yarn knit patternand the repeating nature, if any, of these individual yarn knitpatterns. As depicted in FIG. 12, front yarn 50 f is repeated about 10times and then front yarn 54 f followed by front yarn 54 f are knittedonce. This ten-by-one-by-one pattern is repeated to yield a technicalfront or exterior surface of the textile graft 12. The technical back ofthe textile graft 10 is depicted in FIG. 12 by repeating back yam 54 bfour times followed by repeating back yarns 52 b, 54 b and 52 b andfurther followed by repeating back yarns 50 b four times. This backpattern is repeated to yield the technical back or interior surface ofthe textile graft 12 of the present invention.

The knitting patterns for the front and back yarns are furtherillustrated in FIG. 13. The front and back yarns are interlaced in arelatively loose pattern. This pattern may be generally referred to asan Atlas pattern. A warp knit Atlas pattern is generally characterizedas a warp knit textile in which a set of yarns shifts diagonally one ormore wale per course for several courses, then returns to the originalposition. In FIG. 13 the course direction is indicated as vector 51 andthe warp direction is indicated by vector 53. The knitted pattern of thepresent invention has multiple patterns of diagonally shifting yarns.Such a pattern provides stretchability to the textile graft 12 and alsoprovides resiliency for the textile graft to substantially return to itsquiescent state from its stretched state.

As shown in FIG. 13, front yarns 50 f and back yarns 50 b shiftdiagonally by two needle positions in alternating closed-loops andopen-loop interlacing structures. The remaining front and back yarnsalso have alternating and repeating closed-loop and open-loopinterlacing structures, but have different needle offsets. For example,back yarn 52 b has a closed-loop, an open loop shifted diagonally in athree-by-one needle shift, followed by a closed-loop at a one-by-oneneedle shift, followed by a three-by-one needle shift for an open-loopand then followed by a closed-loop at an one-by-one needle shift. Asused herein, open loops refer to interlacing yarns where a front or aback yarn does not cross over itself in forming the loop. Also, as usedherein, closed-loops refer to interlacing yarns where a front or a backyarn crosses over itself in forming the loop. Other patterns useful withthe practice of the present invention are illustrated in FIG. 13. All ofthe different patterns are generally referred to as Atlas ormodified-Atlas knit stitches because of their diagonally alternating andrepeating patterns.

To knit textile patterns useful with the present invention, doubleneedle bar warp-knitted machine with multiple beams or guide bars isused to form a flat-knitted seamless tubular structure. The threadingpattern for each guide bar is shown below in Table 1, and thearrangement of each needle for the guide bar is shown below in Table 2.

TABLE 1 Guide Bar Threading Details Guide Bar y - Threaded/n - NotThreaded Settings 1 y y y y y y y y y y n n 2 n n n n n n n n n n y n 3y n n n n n n n n n n n 4 n n n n n n n n n n n y 5 y n n n n n n n n nn n 6 y y y y y y y y y y n n

TABLE 2 Guide Bar Positions Guide Bar Positions 14-6/4-4/4-2/2-2/2-0/2-2/2-4/4-4/(repeat once) 22-4/2-2/2-2/2-0/0-2/0-0/0-0/0-2/(repeat once) 32-2/2-0/2-4/4-4/4-4/4-2/4-2/2-2/(repeat once) 40-0/0-2/0-2/2-2/2-2/2-4/2-0/0-0/(repeat once) 54-2/4-4/4-4/4-2/2-0/2-2/2-2/2-4/(repeat once) 62-2/2-0/2-2/2-4/4-4/4-6/4-4/4-2/(repeat once)

The knitted textile graft of the present invention is desirably made ona warp-knitting machine (not shown) using a 14 bar double needle barRaschel knitting machine. A useful number of needles per centimeter forwarp knitting is from about 7 to about 14 (about 18 to about 36 needlesper inch). About 11 needles per centimeter (28 needles per inch) areparticularly suitable. The textile graft is usually made from a yarnhaving count from 30 to 300 denier. Desirably, the range of yarn densityis from about 30 to about 80 denier. A particularly suitable yarn countis about 40 denier. Moreover, the yarn may be a single ply, a double plyor a multi-ply. The term “multi-ply” is used herein to indicate morethan two-ply.

Furthermore, the knitted textile graft of the present invention hasgreater than 350 stitches per square centimeter, for instance from about400 to about 900 stitches per square centimeter (about 2,500 to about6,000 stitches per square inch), to provide compliancy of the graft.Desirably, the present invention has from about 500 to about 700stitches per square centimeter (about 3,200 to about 4,500 stitches persquare inch). Moreover, the knitted textile graft of the presentinvention has from about 20 to about 30 courses or wales per centimeter(about 50 to about 80 courses or wales per inch) to provide compliancyof the graft. Desirably, the present invention has from about 22 toabout 27 courses or wales per centimeter (about 57 to about 67 wales orcourses per inch). The number of courses and wales may be the same ordifferent.

In one aspect of the present invention, the knitted textile graft is aknit structure of a single layer with a two-step Atlas movement. Becauseof the single layer construction the textile wall thickness is minimizedto yield a low profile knitted textile graft. The textile wall thicknessis from about 0.3 to about 0.4 millimeters. Desirably, the textile wallthickness is from about 0.33 to about 0.36 millimeters. Furthermore, theknitted textile graft of the present invention has a burst strength fromabout 10 to about 17 kg/cm² (about 150 psi to about 240 psi). Desirably,the knitted textile graft of the present invention has a burst strengthfrom about 12 to about 14 kg/cm² (about 170 psi to about 200 psi). Thestretchability of the knitted textile graft is 50 to 200 percent at aone-kilogram of load. Knitted textile grafts with a stretchability ofabout 75 to 180 percent at one-kilogram load are also useful.Furthermore, knitted textile grafts with a stretchability of about 100to 140 percent at one-kilogram load are also useful.

In a typical method of warp knitting the back yarn is fed from twoinside beams, each beam being a spool holding a plurality of ends.Outside beams may be used in conjunction with the inside beams; theoutside beams being used for feeding the front yarns. Each outside beamalso has a plurality of ends. It should be noted, however, that theinside beams may be used for feeding the front yarn and the outsidebeams used for feeding the back yarn. Regardless of which beams areused, texturized flat yarn is generally used for both the front and backyarns. The minimum number of beams used in making the textile graft ofthe present invention is 2. A greater number of beams, however, may befound useful for specific applications. Six guide beams or guide barshave been found to be particularly useful with the practice of thepresent invention.

Any type of textile product can be used as yarns for the knitted textilegraft of the present invention. Of particular usefulness in forming theknitted fabric prosthesis of the present invention are syntheticmaterials such as synthetic polymers. Synthetic yarns suitable for usein the present invention include, but are not limited to, polyesters,including PET polyesters, polypropylenes, polyethylenes, polyurethanesand polytetrafluoroethylenes. The yarns may be of the monofilament,multifilament, spun type or combinations thereof The yarns may also beflat, twisted or textured, and may have high, low or moderate shrinkageproperties or combinations thereof

The yarns used in forming the textile grafts of the present inventionmay be flat, twisted, textured or combinations thereof Furthermore, theyarns may have high, low or moderate shrinkage properties or combinationof different shrinkage properties. Additionally, the yarn type and yarndenier can be selected to meet specific properties desired for theprosthesis, such as porosity and flexibility. The yarn denier representsthe linear density of the yarn (number of grams mass divided by 9,000meters of length). Thus, a yarn with a small denier would correspond toa very fine yarn whereas a yarn with a larger denier, e.g., 1000, wouldcorrespond to a heavy yarn. The yarns used with the present inventionmay have a denier from about 20 to about 200, preferably from about 30to about 100. Preferably, the yarns are polyester, such as polyethyleneterephthalate (PET), and more preferably the yarns are one ply, 40denier, 27 filament flat and texturized polyester.

After knitting the textile graft of the present invention is optionallycleaned or scoured in a basic solution of warm water, e.g., about 50° C.to about 65° C. (about 120° F. to about 150° F.), and detergent. Thetextile is then rinsed to remove any remaining detergent.

After the textile graft is optionally scoured, the graft is compacted orshrunk to reduce and control, in part, the porosity of the graft.Porosity of a knitted material is measured on the Wesolowski scale andby the procedure of Wesolowski. In the Wesolowski test, a fabric testpiece is clamped flatwise and subjected to a pressure head of about 120mm. of mercury. Readings are obtained which express the number ofmillimeters of water permeating per minute through each squarecentimeter of fabric. A zero reading represents absolute waterimpermeability and a value of about 20,000 represent approximate freeflow of fluid.

The porosity of the textile graft 12 is often from about 7,000 to about15,000 on the Wesolowski scale after being knitted on the double needlebar Raschel knitting machine. A more desirable porosity is from about 30to about 5,000 on the Wesolowski scale and textile graft is compacted orshrunk in the wale direction to obtain the desired porosity. A solutionof an organic component, such as hexafluoroisopropanol ortrichloroacetic acid, and a halogenated aliphatic hydrocarbon, such asmethylene chloride, is used to compact the textile graft by immersing itinto the solution for up to 30 minutes at temperatures from about 15° C.to about 160° C. Other compacting solutions may suitably be used, suchas those disclosed in U.S. Pat. Nos. 3,853,462 and 3,986,828, whosecontents are incorporated by reference herein.

As noted above, preferably the tubular-knitted graft of the presentinvention is constructed of polyester which is capable of shrinkingduring a heat-set process. For instance, such grafts are typicallyflat-knitted in a tubular form. Due to the nature of the flat-knittingprocess, the tubular graft is generally flat in shape after knitting.Such grafts, however, when constructed of shrinkable polyester yarn, canbe heat set on a mandrel to form a generally circular shape.

Such a heat-setting process is accomplished by first knitting the graftin a seamless tubular form out of a material capable of shrinking duringa heat-setting or similar process. The graft may be preshrunk before itis placed on a mandrel. Preshrinking may be achieved by submitting thewoven graft to moderate temperatures, such as from 90° C. to about 205°C. (about 190° F. to about 400° F.). Usually the graft is placed in amedium for the preshrinking. Such a medium can include withoutlimitation hot water, a chemical fluid, such as methylene chloride, or agas, such as air or carbon dioxide. The graft of the present invention,however, may suitably be made without such a preshrinking of the yarns.

After the graft is knitted or alternatively knitted and preshrunk, thegraft is placed on a mandrel, and heated in an oven at a temperature andtime capable of causing the yarns of the graft to heat set to the shapeand diameter of the mandrel. Preferably polyester yarns are used, andthe heat setting is accomplished at time and temperatures appropriatefor the material. For example, heat setting can be accomplished at about90° C. to about 225° C. (about 190° F. to about 437° F.) for a period ofabout less than an hour. Temperatures in the range of about 130° C. toabout 220° C. (about 260° F. to about 428° F.) are also useful.Desirably, temperatures from about 150° C. to about 215° C. (about 300°F. to about 419° F.) are also useful. Desirably, time periods from about5 to about 30 minutes are useful. More desirably, with time periods fromabout 10 to about 20 minutes are useful. Other methods of heat settingknown in the art may be employed. After such a heat setting process, thegraft can be formed into a shape desired for implantation, having agenerally circular inner lumen.

In another aspect of the present invention stent-graft 10 furtherincludes a non-textile layer 13, as depicted in FIG. 14. The non-textilelayer is circumferentially disposed between textile graft 12 and stent14 and securably attached therebetween. One type of non-textile materialparticularly useful is polytetrafluoroethylene (PTFE). PTFE exhibitssuperior biocompatibility and low thrombogenicity, which makes itparticularly useful as vascular graft material in the repair orreplacement of blood vessels. Desirably the non-textile layer is atubular structure manufactured from expanded polytetrafluoroethylene(ePTFE). The ePTFE material has a fibrous state which is defined byinterspaced nodes interconnected by elongated fibrils. The space betweenthe node surfaces that is spanned by the fibrils is defined as theinternodal distance. When the term expanded is used to describe PTFE, itis intended to describe PTFE which has been stretched, in accordancewith techniques which increase the intemodal distance and concomitantlyporosity. The stretching may be in uni-axially, bi-axially, ormulti-axially. The nodes are spaced apart by the stretched fibrils inthe direction of the expansion.

Desirably, the ePTFE material is a physically modified ePTFE tubularstructure having enhanced axial elongation and radial expansionproperties of up to 600 percent by linear dimension. The physicallymodified ePTFE tubular structure is able to be elongated or expanded andthen returned to its original state without an elastic force existingtherewithin. Such a physically modified ePTFE tubular structure isadvantageously used in conjunction with wire-stent 22 of stent-graft 10.

FIG. 16 is a photomicrograph of a traditionally longitudinally expandedePTFE tubular structure. The tube has been stretched in the longitudinaldirection shown by directional arrow 102, leaving the nodescircumferentially oriented in circumferential direction shown by thedirectional arrow 104. The fibrils 106 are shown as being uniformlyoriented in the longitudinal direction shown by directional arrow 102.Nodes 108 are shown and are uniformly oriented in circumferentialdirection 104.

FIG. 17 is a photomicrograph of the physically modified ePTFE tubularstructure having circumferentially oriented nodes and longitudinallytraversing fibrils. Nodes 110 are shown in the photomicrograph with aset of fibrils with first ends 112 and second ends 114 attached thereto.The fibrils with first ends 112 and second ends 114 are shown in ahingeably rotated position so that they are not substantiallylongitudinally oriented in the direction shown by directional arrow 102as compared to the substantially longitudinally oriented parallel fibrilstructures 106 of FIG. 16. The term “hingeably rotated” and variantsthereof refer to reorientation of previously uniformly oriented linesegments by a change in position of one end of each line segment inrelation to the other end of each segment, which remains fixed; i.e.,the “hinge” about which the other end rotates. The reorientation takesplace without a substantial change in dimension of the line segment.Additional details of the physically-modified ePTFE and methods formaking the same can be found in commonly assigned application titled,“ePTFE Graft With Axial Elongation Properties”, filed on date herewith,attorney docket 498-256, the contents of which are incorporated byreference herein.

FIG. 15 is a partial perspective view of an implantable medical fabric40, another aspect of the present invention. The medical fabric 40 is awarp-knitted textile fabric having Atlas and modified-Atlas patterns asdescribed above. The medical fabric 40 has the features of theabove-described textile graft 12, for instance, a high degree ofstretchability. The medical fabric 40 of the present invention is usefulin intraluminal applications, such as hernia repair.

The invention may be further understood with reference to the followingnon-limiting examples.

EXAMPLES Example 1 Single Layer Knit Tubular Graft With a Two-step AtlasMovement

The following specifications are used to fabricate a solid knittedprosthesis of the present invention.

Yarn Type: Texturized polyethylene terephthalate (PET), 40 denier, 27filaments.

Number of Guide Bars: Six.

Guide Bar Threading Details: (y—Threaded/n—Not Threaded)

Guide Bar No. 1: y/y/y/y/y/y/y/y/y/y/y/n

Guide Bar No. 2: n/n/n/n/n/n/n/n/n/n/y/n

Guide Bar No. 3: y/n/n/n/n/n/n/n/n/n/n/n

Guide Bar No. 4: n/n/n/n/n/n/n/n/n/n/n/y

Guide Bar No. 5: y/n/n/n/n/n/n/n/n/n/n/n

Guide Bar No. 6: y/y/y/y/y/y/y/y/y/y/n/n

Guide Bar Position Details:

Guide Bar No. 1: 4-6/4-4/4-2/2-2/2-0/2-2/2-4/4-4/(repeat once)

Guide Bar No. 2: 2-4/2-2/2-2/0-0/0-2/0-0/0-0/0-2/(repeat once)

Guide Bar No. 3: 2-2/2-0/2-4/4-4/4-4/4-2/4-2/2-2/(repeat once)

Guide Bar No. 4: 0-0/0-2/0-2/2-2/2-2/2-4/2-0/0-0/(repeat once)

Guide Bar No. 5: 4-2/4-4/4-4/4-2/2-0/2-2/2-2/2-4/(repeat once)

Guide Bar No. 6: 2-2/2-0/2-2/2-4/4-4/4-6/4-4/4-2/(repeat once)

Graft Processing:

Subsequent to knitting the textile graft, the material was scoured in abasic solution of warm water (e.g., about 65° C. or about 150° F.) andcleaning detergent. It was then rinsed to remove the cleaning agents.The graft was then compacted with methylene chloride at elevatedtemperatures, for instance about 107° C. or about 224° F., for a shortperiod of time, for instance, three minutes.

Next, the prosthesis was heat-set on stainless steel mandrels to achievethe final desired inside diameter. Typically, the outside diameter ofthe mandrel was twenty to forty percent oversized to impart, in part, ahigh stretch characteristic to the textile graft. Heat setting wasaccomplished in a convection oven at about 212° C. (about 414° F.) forabout 10 minutes.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention.

What is claimed is:
 1. An implantable tubular prosthesis capable oflongitudinal expansion from a quiescent state to an elongated statecomprising: a radially contractible and longitudinally expandabletubular stent having a quiescent diameter and quiescent length capableof longitudinal expansion to the elongated state having an elongatedlength and a contracted diameter, wherein the elongated length isgreater than the quiescent length and the contracted diameter is smallerthan the quiescent diameter, and further wherein said stent is capableof resiliently returning from the elongated state to the quiescentstate; and a tubular knitted tubular graft circumferentially disposedand securably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeters to provide compliancy in thequiescent state.
 2. The prosthesis of claim 1 wherein the elongatedlength is at least about 50 percent by length greater than the quiescentlength; and further wherein the elongated length is no more than about200 percent by length greater than the quiescent length.
 3. Theprosthesis of claim 1 wherein said graft has at least about 500 stitchesper square centimeter; and further wherein said graph has no more thanabout 700 stitches per square centimeter.
 4. The prosthesis of claim 1wherein the elongated length is at least about 100 percent by lengthgreater than the quiescent length; and further wherein the elongatedlength is no more than about 140 percent by length greater than thequiescent length.
 5. The prosthesis of claim 1 wherein said graft issubstantially fluid-tight in the quiescent state.
 6. The prosthesis ofclaim 1 wherein said knit pattern is a warp knitted pattern of yarnsforming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns comprise the interior surface and formloops in the longitudinal direction of said prosthesis, and exterioryarns comprise the exterior surface and are diagonally shifted over oneor more of the interior yarns in an alternating pattern along a width ofsaid prosthesis to engage the interior yarns, and further wherein theinterior yarn alternately interlaces the engaging exterior yarn to formopen loops where the interior yarn does not cross over itself and closedloops where the interior yarn does cross over itself.
 7. The prosthesisof claim 1 wherein said knit pattern is an Atlas or a modified Atlasknit pattern.
 8. The prosthesis of claim 1 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 9. Theprosthesis of claim 1 wherein said graft is a single layer of interlacedyarns.
 10. The prosthesis of claim 1 wherein said graft has a wallthickness of at least about 0.3 millimeters; and further wherein saidgraft has a wall thickness no more than about 0.4 millimeters.
 11. Theprosthesis of claim 1 wherein said graft is securably attached atintermediate positions along the length of said stent.
 12. Theprosthesis of claim 11 wherein said graft non-bulgingly contracts fromthe elongated state to the quiescent state to circumferentially abutsaid stent.
 13. The prosthesis of claim 1 wherein said stent has aninterior circumferential surface and further wherein said graft iscircumferentially disposed to said interior surface.
 14. The prosthesisof claim 1 wherein said stent has an exterior circumferential surfaceand further wherein said graft is circumferentially disposed to saidexterior surface.
 15. The prosthesis of claim 1 further including atubular layer of ePTFE circumferentially disposed and securably attachedto said stent.
 16. The prosthesis of claim 15 wherein said tubular layerof ePTFE is circumferentially disposed between said stent and saidgraft.
 17. The prosthesis of claim 1 wherein said stent is a wire-stent.18. The prosthesis of claim 1 wherein said yarns are selected from thegroup consisting of monofilament yarns, multifilament yearns, spun typeyarns, flat yarns, twisted yarns, textured yarns, and combinationsthereof.
 19. The prosthesis of claim 1 wherein said yarns are selectedfrom the group of materials selected from polyesters, polypropylenes,polyethylenes, polyurethanes, polytetrafluoroethylenes or combinationsthereof.
 20. The prosthesis of claim 19 wherein said polyesters includepolyethylene terephthalate polyesters.
 21. The prosthesis of claim 1wherein said yarns are polyethylene terephthalate polyester texturedyarns having a denier of at least about 30; and further wherein saidpolyethylene terephthalate polyester textured yarns have a denier of nomore than about
 100. 22. The prosthesis of claim 1 wherein said patternhas at least 20 stitches per centimeter in the longitudinal direction ofsaid prosthesis; and further wherein said pattern has no more than about30 stitches per centimeter in the longitudinal direction of saidprosthesis.
 23. The prosthesis of claim 1 wherein said pattern has atleast about 20 stitches per centimeter along the width of saidprosthesis; and further wherein said pattern has no more than about 30stitches per centimeter along the width of said prosthesis.
 24. Animplantable tubular prosthesis capable of radial expansion from aquiescent state to a radially expanded state comprising: a radiallyexpandable and longitudinally contractible tubular stent having aquiescent diameter and quiescent length capable of radial expansion tothe radially expanded state having an expanded diameter and a contractedlength, wherein the expanded diameter is greater than the quiescentdiameter and the contracted length is smaller than the quiescent length;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient radial expansion and resilient longitudinalcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeter to provide compliancy in thequiescent state.
 25. The prosthesis of claim 24 wherein the quiescentlength is at least about 50 percent by length greater than thecontracted length; and further wherein the quiescent length is no morethan about 200 percent by greater than the contracted length.
 26. Theprosthesis of claim 24 wherein said knit pattern is a warp knittedpattern of yarns forming a textile layer having an interior surface andan exterior surface, wherein interior yarns predominate the interiorsurface and form loops in the longitudinal direction of said prosthesis,and exterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yarn alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yarn does cross overitself.
 27. The prosthesis of claim 24 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 28. Theprosthesis of claim 24 wherein said graft is a single layer ofinterlaced yarns.
 29. The prosthesis of claim 24 wherein said graft hasa wall thickness of at least 0.3 millimeters, and further wherein saidgraft has a wall thickness no more than 0.4 millimeters.
 30. Theprosthesis of claim 24 further including a tubular layer of e-PTFEcircumferentially disposed and securably attached to said stent.
 31. Theprosthesis of claim 24 wherein said stent is a slotted-stent.
 32. Theprosthesis of claim 24 wherein said yarns are polyethylene terephthalatepolyester textured yarns having a denier of at least about 30; andfurther wherein said polyethylene terephthalate polyester textured yarnshave a denier no more than about
 80. 33. The prosthesis of claim 24wherein said graft is longitudinally stretched to circumferentiallyencompass said stent in the quiescent state of said prosthesis.
 34. Animplantable tubular prosthesis capable of longitudinal expansion from aquiescent state to an elongated state comprising: a radiallycontractible and longitudinally expandable tubular stent having aquiescent diameter and quiescent length capable of longitudinalexpansion to the elongated state having an elongated length and acontracted diameter, wherein the elongated length is greater than thequiescent length and the contracted diameter is smaller than thequiescent diameter, and further wherein said stent is capable ofresiliently returning from the elongated state to the quiescent state;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having at leastabout 400 stitches per square centimeter and further having no more thanabout 900 stitches per square centimeter to provide compliancy in thequiescent state; wherein said knit pattern is a warp knitted pattern ofyarns forming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns predominate the interior surface andform loops in the longitudinal direction of said prosthesis, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yarn alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yarn does cross overitself.
 35. The prosthesis of claim 34 wherein the elongated length isat least about 50 percent by length greater than the quiescent length;and further wherein the elongated length is no more than about 200percent by length greater than the quiescent length.
 36. The prosthesisof claim 34 wherein said knit pattern comprising a interior and exterioryarns interlaced from single stitches, said single stitches beingdeposed in a plurality of stitch repeating patterns, wherein a firststitch has a repeating pattern traversing diagonally by two or moreneedle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 37. The prosthesis of claim 34 whereinsaid graft has a wall thickness of at least about 0.3 millimeters; andfurther wherein said graft has a wale thickness of no more than about0.4 millimeters.
 38. The prosthesis of claim 36 further including atubular layer of e-PTFE circumferentially disposed and securablyattached to said stent.
 39. The prosthesis of claim 34 wherein saidstent is a wire-stent.
 40. The prosthesis of claim 34 wherein said yarnsare polyethylene terephthalate polyester textured yarns having a denierfrom about 30 to about
 100. 41. An implantable tubular prosthesiscapable of longitudinal expansion from a quiescent state to an elongatedstate comprising: a radially contractible and longitudinally expandabletubular stent having a quiescent diameter and quiescent length capableof longitudinal expansion to the elongated state having an elongatedlength and a contracted diameter, wherein the elongated length isgreater than the quiescent length and the contracted diameter is smallerthan the quiescent diameter, and further wherein said stent is capableof resiliently returning from the elongated state to the quiescentstate; and a tubular knitted tubular graft circumferentially disposedand securably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having greater thanabout 350 stitches per square centimeter to provide compliancy in thequiescent state; wherein the elongated length is at least 50 percent bylength greater than the quiescent length; and further wherein theelongated length is no more than about 200 percent by length greaterthan the quiescent length.
 42. The prosthesis of claim 41 wherein saidknit pattern is a warp knitted pattern of yarns forming a textile layerhaving an interior surface and an exterior surface, wherein interioryarns predominate the interior surface and form loops in thelongitudinal direction of said prosthesis, and exterior yarnspredominate the exterior surface and are diagonally shifted over one ormore of the interior yarns in an alternating pattern along a width ofsaid prosthesis to engage the interior yarns, and further wherein theinterior yarn alternately interlaces the engaging exterior yarn to formopen loops where the interior yarn does not cross over itself and closedloops where the interior yarn does cross over itself.
 43. The prosthesisof claim 41 wherein said knit pattern comprising a interior and exterioryarns interlaced from single stitches, said single stitches beingdeposed in a plurality of stitch repeating patterns, wherein a firststitch has a repeating pattern traversing diagonally by two or moreneedle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 44. The prosthesis of claim 41 furtherincluding a tubular layer of ePTFE circumferentially disposed andsecurably attached to said stent.
 45. The prosthesis of claim 41 whereinsaid stent is a wire-stent.
 46. The prosthesis of claim 41 wherein saidyarns are polyethylene terephthalate polyester textured yarns having adenier of at least 30; and further wherein said polyethyleneterephthalate polyester textured yarns have a denier of no more thanabout
 100. 47. An implantable tubular prosthesis capable of longitudinalexpansion from a quiescent state to an elongated state comprising: aradially contractible and longitudinally expandable tubular stent havinga quiescent diameter and quiescent length capable of longitudinalexpansion to the elongated state having an elongated length and acontracted diameter, wherein the elongated length is greater than thequiescent length and the contracted diameter is smaller than thequiescent diameter, and further wherein said stent is capable ofresiliently returning from the elongated state to the quiescent state;and a tubular knitted tubular graft circumferentially disposed andsecurably attached to said stent in the quiescent state, said grafthaving a pattern of yarns interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of said graft to the elongated state and having greater thanabout 350 stitches per square centimeter to provide compliancy in thequiescent state; wherein said interlaced stitches of said graft form agraft wall and further wherein said graft wall has a wall thickness ofat least 0.3 millimeters; and further wherein said graft wall has a wallthickness of no more than about 0.4 millimeters.
 48. The prosthesis ofclaim 47 wherein said knit pattern is a warp knitted pattern of yarnsforming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns predominate the interior surface andform loops in the longitudinal direction of said prosthesis, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said prosthesis to engage the interior yarns, andfurther wherein the interior yam alternately interlaces the engagingexterior yarn to form open loops where the interior yarn does not crossover itself and closed loops where the interior yam does cross overitself.
 49. The prosthesis of claim 47 wherein said knit patterncomprising a interior and exterior yarns interlaced from singlestitches, said single stitches being deposed in a plurality of stitchrepeating patterns, wherein a first stitch has a repeating patterntraversing diagonally by two or more needle positions and a secondstitch has a repeating pattern alternatively traversing diagonally bythree or more needle positions and then by one needle position.
 50. Theprosthesis of claim 47 further including a tubular layer of ePTFEcircumferentially disposed and securably attached to said stent.
 51. Theprosthesis of claim 47 wherein said stent is a wire-stent.
 52. Theprosthesis of claim 47 wherein said yarns are polyethylene terephthalatepolyester textured yarns having a denier of at least about 30; andfurther wherein said polyethylene terephthalate polyester textured yarnshave a denier of no more than about
 80. 53. An implantable tubular graftcomprising: a tubular knitted tubular graft having a pattern of yarnsinterlaced into stitches in a knit pattern capable of resilientlongitudinal elongation and resilient radial contraction of said graftfrom a quiescent state to the elongated state and having at least about400 to 900 stitches per square centimeter and further having no morethan about 900 stitches per square centimeter to provide compliancy inthe quiescent state, wherein said knit pattern is a warp knitted patternof yarns forming a textile layer having an interior surface and anexterior surface, wherein interior yarns predominate the interiorsurface and form loops in the longitudinal direction of said graft, andexterior yarns predominate the exterior surface and are diagonallyshifted over one or more of the interior yarns in an alternating patternalong a width of said graft to engage the interior yarns, and furtherwherein the interior yarn alternately interlaces the engaging exterioryarn to form open loops where the interior yarn does not cross overitself and closed loops where the interior yarn does cross over itself.54. The graft of claim 53 wherein said knit pattern comprising ainterior and exterior yarns interlaced from single stitches, said singlestitches being deposed in a plurality of stitch repeating patterns,wherein a first stitch has a repeating pattern traversing diagonally bytwo or more needle positions and a second stitch has a repeating patternalternatively traversing diagonally by three or more needle positionsand then by one needle position.
 55. The graft of claim 53 wherein saidyarns are polyethylene terephthalate polyester textured yarns having adenier of at least 30; and further wherein said polyethyleneterephthalate polyester textured yarns having a denier of no more than80.